This section provides background information related to the present disclosure which is not necessarily prior art.
In a lighting apparatus using a PN junction light-emitting element, a light-emitting diode (LED) module having a plurality of LEDs mounted on a power transmitting substrate is typically used as a light source. The LEDs have the advantages of small size, low power consumption and excellent control characteristics, and therefore the LED lighting apparatus can be made slim and lightweight. However, a typical LED lighting apparatus includes a heat sink for heat dissipation or a separate drive circuit for driving an LED module. Elements such as the heat sink or the drive circuit make it difficult to realize a slim and lightweight design of the LED lighting apparatus.
For example, the drive circuit may include an A/D converter to supply DC power, and the A/D converter includes a trans-coil for lowering the voltage of AC. The trans-coil has a drawback in that, since the trans-coil is arranged occupying a large space in the drive circuit, the dimension of the product having the same becomes large.
In order to solve the problems as described above, a power supply device called a switching mode power supply (SMPS) has been recently employed. Here, the SMPS transforms an AC frequency (50 Hz-60 Hz) into a DC frequency, so it requires a high level of technologies.
However, it is necessary for a conventional LED driver using an SMPS to have a noise filter because it uses high-speed switching and hence generates much noise. Besides, it is difficult to configure a circuit at a low cost because a lot of parts are used for circuit configuration. Additionally, the SMPS itself occupies a fairly large size compared to the size of an LED module. As a result, there are limitations on the miniaturization of the LED module and thus of the product itself.
Meanwhile, since the LED module includes a plurality of LEDs, the overall current capacity becomes large. Thus, the conventional LED drive circuit employs an electrolytic capacitor as a part. Such an electrolytic capacitor is suitable for a circuit with high capacitance, but its poor frequency characteristics and relatively high aging degradation reduce the reliability of the circuit. Particularly, in the case of an electrolytic capacitor being mounted, together with an LED, on a power transmitting substrate, the lifespan of the electrolytic capacitor is much shortened due to heat generated by light emission of the LED. Moreover, as the volume of an inductor and a capacitor increases in a circuit having a plurality of LEDs arranged thereon, this may even cause limitations to the exterior design of an LED lighting apparatus.
In addition, as an example of the conventional lighting apparatus, disclosed is a lighting apparatus in which a plurality of PN junction light-emitting elements are arranged in both directions, with their rows being connected in parallel, and used directly for an AC power source without using a separate drive circuit. Voltage is adjusted as needed via a resistor. The PN junction light-emitting elements in one direction emit light when a positive (+) voltage is applied thereto, and the PN junction light-emitting elements in the opposite direction emit light when a negative (−) voltage is applied thereto.
Such a lighting apparatus is advantageous in that a lighting apparatus using a PN junction light-emitting element can be easily implemented without using a separate drive circuit for converting AC into DC, but poses a problem in the use of a dimmer (see FIG. 2). For instance, if light is dimmed to 5V when 10V is required to drive the PN junction light-emitting elements connected in series, no current conduction occurs. If a dimmer adapted to set the conduction time by on/off is used, the PN junction light-emitting elements basically emit no light at 10V or less so that their emission time is limited. In addition, the conduction time limitation imposed by the dimmer may cause problems such as flickering.